Diverse yet endangered: pollen dispersal and mating system reveal inbreeding in a narrow endemic plant

Background: Mating system and allele dispersal through pollen and seeds influence population genetic constitution and are directly associated with structure and diversity. Petunia secreta is a rare and endemic species that is characterised by high levels of genetic variability and, despite being dependent on bee-pollination, its breeding system is unknown. Aims: In order to understand how a rare and narrowly distributed species presents levels of genetic diversity compatible with that of widely distributed congeneric species, the aims of this study were to investigate the mating system of P. secreta; to evaluate its pollen and seed dispersal; and to estimate the level of inbreeding. Methods: We geographically mapped and genotyped all adult individuals from the type origin of P. secreta during one reproductive season and 125 offspring originating from 11 mother plants at nine polymorphic microsatellite loci and using population genetics tools and paternity analysis. Results: No geographical structure was observed in adult individuals. The species has mixed mating system, with predominant self-fertilisation and few outcrossing events. All outcrossing events occurred within the respective maternal plant's collection site. High, positive F-is values were observed among adult plants, and inbreeding depression was observed in progenies. Conclusions: In the long term, the main threat for this species consists of the high level of inbreeding depression resulting mainly from the biparental inbreeding, which affects the genetic diversity. These results should be considered in the development of strategies for in situ species conservation.